1. Field of the Invention
The present invention relates to a module structure of a dye sensitized solar cell.
2. Description of the Related Art
A photovoltaic power system is actively being developed in order to promote effective utilization of natural energy. Currently a solar cell which generates photovoltaic power has been mainly made from single-crystal or poly-crystalline silicon. However, the photovoltaic power generation has not yet led to become widespread because of unstable supply of raw silicon or insufficient cost reduction in process.
The dye sensitized solar cell which is created by professor Graetzel of Switzerland receives attention as a low-cost solar cell because silicon is not used as the raw material. A sectional view of a conventional dye sensitized solar cell is schematically shown in FIG. 4. The dye sensitized solar cell includes a transparent conductive oxide 23, a dye-adsorbed semiconductor thin film 33 which is adjacent to the transparent conductive oxide 23, a counter electrode 43, and an electrolytic solution 51.
The transparent conductive oxide 23 is used as a light acceptance-side electrode. Generally, the transparent conductive oxide 23 is produced by depositing a conductive metal oxide 22 on a transparent substrate 21 made of soda lime glass. FTO (Fluorine-doped Tin Oxide) or ITO (Indium Tin Oxide) is used as the conductive metal oxide 22.
The dye-adsorbed semiconductor thin film 33 includes a metal oxide 31 such as a titanium oxide having a semiconductive property which is formed into porous shape and is adjacent to the conductive metal oxide 22, and a sensitizing dye 32 is supported on a surface of the metal oxide 31.
The counter electrode 43 includes a conductive substrate 41 and a catalytic layer 42 which promotes a chemical reaction of an electrolyte and is supported on the conductive substrate 41. The catalytic layer 42 includes platinum or carbon.
The counter electrode 43 and the dye-adsorbed semiconductor thin film 33 retained by the transparent conductive oxide 23 are disposed so as to face each other, and a sealing agent 61 is applied to a peripheral portion of the substrate with a predetermined gap. The two electrodes 22 and 43 are bonded to each other with the sealing agent 61 interposed therebetween, thereby producing a cell. An electrolyte containing a redox mediator which is made of iodine and an iodide ion is charged into the gap between the electrodes 22 and 43 through an electrolytic filling hole 71 to form a charge transporting electrolytic solution 51.
A nitrile organic solvent having a relatively large dielectric constant is mostly used as the electrolytic solution 51. There is an attempt to use an ambient temperature molten salt (ionic solution) to prevent volatilization of the electrolyte. In a mobile liquid, there is a risk of leakage during production or cell breakage. Therefore, an attempt to quasi-solidify the mobile liquid, that is, to turn into a gel is provided to prevent the leakage of the mobile liquid.
For enlargement of the dye sensitized solar cell, because the metal oxide 22 deposited on the transparent conductive oxide has a sheet resistance as large as several Ω/□, a series resistance of the cell is increased as the dye sensitized solar cell is enlarged. Therefore, generally a collector electrode is placed in the transparent conductive oxide 23. A sectional view of a conventional dye sensitized solar cell in which a collector electrode is provided is schematically shown in FIG. 5. There are various collector electrode structures. Generally, a metal grid 81 is provided adjacent to the metal oxide 22, and a protective layer 82 is provided such that the metal grid 81 does not contact the electrolytic solution 51 (for example, see Japanese Patent Application Laid-Open No. 2003-203682).
Generally, the redox mediator containing the iodine and iodide ion is used as the electrolyte of the dye sensitized solar cell. Because many kinds of metals are corrosive for the redox mediator containing the iodine and iodide ion, it is necessary to protect the metal grid 81. A dielectric material such as a resin and glass frit is used as the protective layer 82.
In order to enhance efficiency of the enlarged dye sensitized solar cell, it is necessary to decrease the increased electric resistance caused by the enlargement. The increased electric resistance caused by the enlargement can mainly be divided into the sheet resistance of the metal oxide of the transparent conductive oxide and a dielectric resistance of the electrolyte which is increased in proportion to a distance between the transparent conductive oxide and the counter electrode. Although the sheet resistance can be decreased by placing the collector electrode, it is necessary to devise a sectional structure of the solar cell in the distance between the transparent conductive oxide and the counter electrode.
However, the collector electrode, the protective layer, and the like are provided in the transparent conductive oxide to complicate the structure. Therefore, a corner portion of the protective layer is broken when the distance with the counter electrode is shortened, which possibly causes a short circuit of the solar cell. In order to prevent the short circuit, it is necessary to obtain the dye sensitized solar cell in which the distance between the transparent conductive oxide and the counter electrode is shortened as much as possible without generating the breakage of the protective layer which causes the short circuit.